The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
There are many devices for transmitting torque known in the art. Examples include hydraulically actuated clutch plates, dog clutches actuated by shift forks, one-way clutches, and selectable one-way clutches. These devices are able to transmit torque between two separate components, and each is useful for its intended purpose.
The one-way clutch is used in many applications for transmitting torque in one rotational direction. A typical one-way clutch may include an inner ring disposed within an outer ring. A connecting member is located between the rings for selectively transmitting torque between the rings. The connecting member may take various forms, for example, a sprag, roller, or rocker. The connecting member acts to engage the rings in order to transmit torque when one of the rings is rotated in a first direction relative to the other of the rings. If the rings are rotated in an opposite relative direction, the connecting member does not engage the rings, and torque is not transmitted through the one-way clutch. In this way the one-way clutch is effective in transmitting torque between two components.
One type of brake or clutch useful in automatic transmissions is known as a selectable one-way clutch, which allows different torque settings to be selected. For example, a selectable one-way clutch may include one setting to function as a one-way clutch and another setting which allows the inner ring and the outer ring to rotate freely relative to one another in both directions. In another example, a selectable one-way clutch may include one setting to function as a one-way clutch and another setting which allows torque to be transmitted between the inner ring and the outer ring in both directions. A selectable one-way clutch is similar to a basic one-way clutch, which includes a “locked” mode in one rotational direction and a “freewheel” mode in the opposite rotational direction. In the basic one-way clutch, the operating mode is determined by the direction of the torque being applied to the input member. A selectable one-way clutch is further capable of producing a driving connection between an input member and an output member in one or both rotational directions and is also able to freewheel in one or both rotational directions as needed. As an example, a selectable one-way clutch may be implemented to transfer torque from an engine to the transmission, and to interrupt the transfer of reverse torque from the transmission to the engine.
Selectable one-way clutches in automatic transmissions may employ a high pressure hydraulic control system that is used to actuate the selectable one-way clutch. However, there are applications, such as hybrid electric vehicles, that may not otherwise require a high pressure hydraulic control system. Selectable one-way clutches also often require high spring forces, which may result in a large amount of drag. It is desirable, however, to avoid a large amount of drag in order to improve fuel economy. Accordingly, there exists a need for a low-drag selectable one-way clutch.